1. Field of the Invention
The present invention relates to a fuel injection control method which can determine an injection timing of a fuel by a simple system in the case of supplying the fuel to a four-cycle engine on the basis of one injection per two rotations by using an electronic control type fuel injection apparatus.
2. Description of the Related Art
As one method of determining an injection timing of the fuel in the case of supplying the fuel to the four-cycle engine by using the electronic control type fuel injection apparatus, Japanese Unexamined Patent Publication No. 2002-364435 describes a technique of utilizing a primary voltage of an ignition coil as a signal for determining the injection timing in a structure employing a fixed spark advance ignition system in synchronous with an engine rotation. In other words, the technique described in this publication is structured such that a magnet is provided at a predetermined position in an outer peripheral portion of a flywheel attached to a crank shaft of an engine, an ignition coil is arranged at an opposing position in an outer periphery, a spark is generated in an ignition plug on the basis of a secondary voltage generated by a voltage induced in the ignition coil by the magnet per one rotation of the flywheel, and the primary voltage of the ignition coil is picked up so as to be utilized as the signal for determining the injection timing.
In accordance with this method, since the method uses the primary voltage of the ignition coil in the fixed spark advance ignition system using the flywheel, there is an advantage that the structure is extremely simple and can be inexpensively provided. However, since one injection is performed per one rotation in this structure, there is a risk that a working frequency of the fuel injection valve is twice of the structure in which one injection is performed per two rotations of the engine, thereby generating a problem in a durability, and an ineffective pulse width of the fuel injection valve becomes twice, whereby it is hard to secure a dynamic range. In addition, if a fuel injection valve having a low discharge pressure is used and is injected in an intake stroke of the engine, an atomization of the fuel is effectively performed, so that it is possible to intend to improve a fuel stability. However, since the intake stroke can not be specified by the method mentioned above, it is improper to use the fuel injection valve having the low discharge pressure.
As the other method of determining the injection timing of the fuel in the four-cycle engine, Japanese unexamined Patent Publication No. 2001-207902 describes a technique of discriminating what stroke the cylinder of the engine exists on the basis of a crank angle of the engine and an intake pipe pressure so as to determine the injection timing. In other words, the technique described in this publication uses a crank angle sensor in which a timing rotor having a lot of projection portions in an outer peripheral surface is attached to a crank shaft of the engine, and a pickup coil is arranged at an opposing position in an outer periphery thereof, and an intake pipe pressure sensor, discriminates that the engine is in an intake stroke, particularly, in a starting time thereof on the basis of signals from these two sensors or discriminates that the engine is in a compression stroke, particularly, in a starting time thereof, thereby determining the injection timing.
In accordance with the method, it is possible to determine the injection timing of one injection per two rotations at a desired time, for example, the injection is finished before the intake stroke or the like. However, since this structure uses the crank angle sensor and the intake pipe pressure sensor so as to discriminate the stroke of the engine and output the predetermined injection signal and ignition signal to the fuel injection valve ignition coil, it is determined an ignition spark advance property without using a cam shaft phase detecting sensor, however, since the crank angle sensor is necessary in addition to the ignition coil, the structure is not satisfactory in achieving an object that an inexpensive structure is provided by reducing a number of constituting parts.
The present invention intends to achieve the problem that it is impossible to supply the fuel to the four-cycle engine, particularly, of a single cylinder, on the basis of one injection per two rotations, and to ignite and burn in accordance with a fixed spark advance system, by the prior art mentioned above, and an object of the present invention is to determine a timing of the injection performed at one time per two rotation in accordance with an extremely simple procedure.